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Preparation and Properties of Cement-based Self-Ieveling Mortar ZHANG Shu-peng , LI Dong-xu

Influence of ultra-early strengthening type polycarboxylate water-reducers

on the performance of precast concrete of metro segments Li Chongzhi, Zhang Fangcai, Wei Gongxiao, Zhang Yong

Conceptual Model of Fresh Cement Paste and Cause Analysis for Concrete

Bleeding Li chongzhi, Zhang fangcai , Liao wei, Ma jian, Ge tinglin

Effects of air-entraining agents and Welan gum on rheological properties

of fresh cement mortar KE Guo-ju, TlAN So, WANG Ji-liang

In-situ 'H-TD-NMR a suitable method for insights into polyrner cernent

interactions during hydration Dominique Ectors, Friedlinde Goetz-Neunhoeffer, Wolf-Dieter Hergeth, Ulf Dietrich, Jürgen Neubauer

Reactivity and cementitious properties of copper tailings by rnicrowave

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irradiation 376 Zhang Changsen, Zhou Tingting, Zhang Jianli,Wu Qisheng Zbu Huajun

CNT-stabilized foam concrete on the basis of ultra high performance concrete

~&q 3n Christina Kramcr, Matthias Schauerte, Torsten Kowald, Reinhard Trettin

Investigation on Properties and Pozzolanic Reaction Degree of Volcanic

Rocks from Eastern Jiangxi Province, China Lehua Yu, Shuangxi Zhou, and Cailing Xu

Monitoring the Cement Flocculation in Freshly Mixed Cement Paste Jae Hong Kim, Hong Jae Yim

Cement Compatibility of PCE Superplasticizers LangeA., Lei L. , Plank J.

Research on Pulverized coal Cornbustion Characteristics of Different

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Oxygen Concentrations 381 ZHU Wen-shang, YAN Si-Ian, Q[ Yan-yong, WANG Jun-jie,WANG Lan,SONG Juo-hua

Photocatalytic performance of calcium aluminate cements modified with Ti02 382 Pérez-Nicolás, M., Navarro-Blasco, l., Duran, A., Sirera, R., Fernández, J.M., Alvarez, 1.1.

Impact of Guar Gurn Derivatives on Properties of Freshly-Mixed

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Modified Lignin as Concrete Superplasticizer Tapio Vehmas, Afina Kalliola ,Tarja Tamminen,Tiina Liitia.

Hydration and Microstructure Development in Accelerated Cement

Pastes Produced by Spraying for the Evaluation of Shotcrete Renan P Salvador, Sergio H P Cavalaro, Ángel Rueda, Antonio D de Figuciredo

Effect of water-entraining adrnixtures on the hydro-mechanical properties

of ultra-high performance concrete

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Photocatalytic performance of calcium aluminate cements modified with TiO2

Results

Introduction

The main aim of this work* is to obtain for the first time depolluting calcium aluminate cement (CAC) modified with different amounts of TiO2 in order to remove NO and NO2 (NOx) from the atmosphere. These toxic gases thatcaused atmospheric pollution, could be removed by a photochemical oxidation assisted process through TiO2 . So TiO2 incorporation as photocatalytic additive in building materials has increased in the last years although hisactivity in CAC has not yet been addressed.The aim of this work is to obtain depolluting and self-cleaning CAC mortars modified with different amounts of TiO2.

Material and Methods

Mortar specimens of two types of CAC (one type of CAC was low alumina cement (L-CAC) with 17.0 wt. % in Fe2O3, and the other one contains high alumina percentages (H-CAC) with only a 0.1 wt. % in Fe2O3.). Normalcuring condition (20°C and 95% RH) was imposed to half of the samples and the second curing condition (hereinafter, forced curing condition), with high temperatures and RH (60°C and 100% RH, and after 24h, 20°C and95% RH) to the rest of the samples.Mineralogical characterization was carried out by X-ray diffraction and textural characteristics as well as elemental composition were performed by means of SEM-EDAX studies.Photocatalytic activity of TiO2 was assessed on mortar samples irradiated with UV radiation and exposed to an air flow composed of NO (1000 ppbv) and NO2 (50-200 ppbv). The accurate measurement of the concentrationof NO and NO2 was carried out through a chemiluminescence analyser. Photocatalytic activity was also evaluated in the visible region adding Methyl Orange solution and measuring the colour loss by a spectrophotometerusing colour coordinates in the CIELab colour space.

Pérez-Nicolás, M. 1 , Navarro-Blasco, I.1, Duran, A. 1, Sirera, R. 1, Fernández, J.M. 1, Alvarez, J.I. 1*

1. MIMED Research Group, Department of Chemistry and Soil Sciences, University of Navarra, 31008 – Pamplona, Spain

Conclusions

Results indicate:• XRD and SEM studies show an interaction between the ferrite (brownmillerite) phase present in the L-CAC with the TiO2 added, is the responsible of the formation of certain amounts of titanates, mainly

pseudobrookite. This phases present more reduce band gap than TiO2, so its photocatalytic activity is higher under visible irradiation.• Better NO abatements under UV irradiation are seen in H-CAC samples because of the lack of reduce band gap phases.• However, these new phases allowed L-CAC samples to show better photocatalytic activity under visible irradiation, as confirmed by degradation of methyl orange.

Cement Al2O3 (%) CaO (%) Fe2O3 (%) SiO2 (%) SO3 (%) Na2O+K2O (%) Main mineralogical phases Minor mineralogical phases

L-CAC 42.0 37.8 17.0 3.0 0.1 0.1 CaAl2O4 (CA)Ca2FeAlO5 (C4AF), Ca12Al14O33 (C12A7), ß-Ca2SiO4 (C2S),

Ca3TiFe2O8, FeO

H-CAC 70.9 28.0 0.1 0.2 ≺0.3 ≺0.5 CaAl2O4, (CA), CaAl4O8 (CA2) Ca12Al14O33 (C12A7)

Table 1. Chemical and mineralogical composition of the L-CAC and H-CAC

Figure 1. XRD studies of H-CAC showed the absence of any new distinct crystalline phase involving TiO2,indicating that no strong chemical interaction took place upon addition of the TiO2 in these samples. In 10 wt. %TiO2-loaded H-CAC sample, the anatase peaks were identified. Nevertheless, for L-CAC samples, the diffractionpeak of anatase almost completely disappeared and the presence of pseudobrookite and ilmenite phases is seen as aconsequence of the interaction between TiO2 and ferrite (brownmillerite) phase.

Figure 2. Plain L-CAC samples as well as H-CAC samples present similar textural appearance (with fracturedsurfaces and with some well identified compounds, such as hexagonal plate-like crystals of C2AH8 metastablecalcium aluminates. The addition of 5 wt.% of TiO2 resulted in a different micro-morphology depending on thetype of cement: for L-CAC samples irregular and non-geometric aspect were seen with some ill-defined clusters,under normal curing regime. Nevertheless, SEM studies let us see prismatic crystals with well-defined structures inH-CAC samples.

Figure 3. Profiles of NO, NO2 and NOx abatements for H-CAC samples loaded with 5 wt.% TiO2 under normaland forced curing condition. Three common stages are seen: i) in the absence of UV radiation the concentration of NOand NOx was kept constant during the first 10 min. ii) Under UV radiation (30 min) the heterogeneous photocatalysisreaction took place iii) When the UV radiation was off, the NO/NOx concentration returned to its initial value. Contrary towhat is usually observed in previous works dealing with photocatalytic portland cement mortars the NO2 gas profiledecreased under UV radiation. This fact has been related to a photoadsorption plus reaction mechanism owing to thealuminates presence.

Figure 4. Percentages of NO abatements. H-CAC abatements are clearly greater than L-CAC ones due to the absence ofiron phases. The higher dosage of additive, the higher NO removal.

Figure 5. Color variation of methyl orange-treated samples under visible light irradiation in a) TiO2-doped H-CAC and b) TiO2-doped L-CAC samples. Contrary to NO abatement results, photocatalytic activity was lower for H-CAC samples than for L-CACowing to the lack of more reduced band gap phases as pseudobrookite (2,18 eV).

Acknowledgements

The authors want to thank Ciments Molins and Kerneos España for the material supplied. This work was funded by Fundación Universitaria de Navarra (grant FUNA2013-15108402) and by Fundación CajaNavarra (under grant 31-2014). M. Pérez also gratefully acknowledges Friends of University of Navarra Inc. for a pre-doctoral grant.

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*Pérez-Nicolás M, Balbuena J, Cruz-Yusta M, Sánchez L, Navarro-Blasco Í, Fernández JM, Álvarez JI. Photocatalytic NOx abatement by calcium aluminate cements modified with TiO2 : improved NO2 conversion. CemConcr Res 2015;70:67-76.